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Date: Sun, 21 Feb 2016 14:41:21 +0300 (MSK)
From: Alexander Monakov <amonakov@...ras.ru>
To: musl@...ts.openwall.com
Subject: [RFC PATCH] micro-optimize __procfdname
Hello,
I've noticed that internal function __procfdname can be slightly cleaned up by
filling the supplied buffer right-to-left and returning the last filled
position. The patch below implements what I have in mind, and changes one
call site to demonstrate (I'll be happy to submit a patch that converts all
calls, if overall this change is desirable).
diff --git a/src/internal/procfdname.c b/src/internal/procfdname.c
index 697e0bd..cfb3f90 100644
--- a/src/internal/procfdname.c
+++ b/src/internal/procfdname.c
@@ -1,13 +1,9 @@
-void __procfdname(char *buf, unsigned fd)
+char *__procfdname_impl(char *buf, unsigned fd)
{
- unsigned i, j;
- for (i=0; (buf[i] = "/proc/self/fd/"[i]); i++);
- if (!fd) {
- buf[i] = '0';
- buf[i+1] = 0;
- return;
- }
- for (j=fd; j; j/=10, i++);
- buf[i] = 0;
- for (; fd; fd/=10) buf[--i] = '0' + fd%10;
+ *buf = 0;
+ do *--buf = '0' + fd % 10;
+ while (fd /= 10);
+ for (int i = 13; i >= 0; i--)
+ *--buf = "/proc/self/fd/"[i];
+ return buf;
}
diff --git a/src/internal/procfdname.h b/src/internal/procfdname.h
index e69de29..6d3c6e2 100644
--- a/src/internal/procfdname.h
+++ b/src/internal/procfdname.h
@@ -0,0 +1,9 @@
+#ifndef PROCFDNAME_H
+#define PROCFDNAME_H
+
+char *__procfdname_impl(char *, unsigned);
+
+#define procfdbufsize sizeof "/proc/self/fd/0123456789" + (3 * (sizeof(int)-4))
+#define procfdname(buf, fd) __procfdname_impl(buf + procfdbufsize - 1, fd)
+
+#endif
diff --git a/src/process/fexecve.c b/src/process/fexecve.c
index 6507b42..88e6b9d 100644
--- a/src/process/fexecve.c
+++ b/src/process/fexecve.c
@@ -1,13 +1,11 @@
#include <unistd.h>
#include <errno.h>
-
-void __procfdname(char *, unsigned);
+#include "procfdname.h"
int fexecve(int fd, char *const argv[], char *const envp[])
{
- char buf[15 + 3*sizeof(int)];
- __procfdname(buf, fd);
- execve(buf, argv, envp);
+ char buf[procfdbufsize];
+ execve(procfdname(buf, fd), argv, envp);
if (errno == ENOENT) errno = EBADF;
return -1;
}
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